Data recording device and data reproducing device

ABSTRACT

The present invention provides a data recording device that can restrain the low-pass component in data to be written onto a recording medium without causing a problem in decoding the data using likelihood information. This data recording device includes: a data bit string combining unit that combines, by predetermined combining rules, a plurality of predetermined parity bit strings one by one with a data bit string obtained prior to a change to the bit order in a bit order rearranging procedure, thereby generating a plurality of composite data bit strings; and a data bit string selecting unit that selects one encoded data bit string from a plurality of encoded data bit strings generated through encoding procedures including the bit order rearranging procedure carried out for each of the plurality of composite data bit strings. Based on the selected encoded data bit string, the data recording device performs a data write operation onto the recording medium.

BACKGROUND OF THE INVENTION

The present invention generally relates to data recording devices suchas magnetic disk devices, optical disk devices, and magnetic tapedevices, and, more particularly, to a data recording device thatrearranges and records data strings on a recording medium that can beset to a data reproducing device that reproduces recorded data inaccordance with likelihood information generated from a reproductionsignal.

The present invention also relates to a data reproducing device that issuitable for reproducing data from a recording medium on which data isrecorded by the above data recording device.

A method of rearranging (interleaving) data in an encoding process hasbeen employed as a technique for preventing burst errors in restoredsignals in a decoding process. A turbo encoding process and a repetitivedecoding process have been used as an encoding and decoding techniquerespectively using the data rearranging method.

Turbo encoding is an encoding technique with a great encoding gain, andhas been widely used in the field of communications. A turbo encodingdevice generally has two recursive structure convolution encoders forencoding a data bit string u, as shown in FIGS. 1 and 2.

In FIG. 1, the turbo encoding device includes a first encoder 11, aninterleaver (π1) 12, a second encoder 13, and a combining unit 14. Thedata bit string u is supplied to the first encoder 11 and the secondencoder 13 via the interleaver (π1) 12.

The first encoder 11 and the second encoder 13 are recursive structureconvolution encoders. The first encoder 11 generates a parity bit stringp1 from the supplied data bit string u. The interleaver (π1) 12 outputsa signal string having a different bit order from the inputted data bitstring u. The second encoder 13 generates a parity bit string p2 fromthe signal string supplied from the interleaver (π1) 12.

The combining unit 14 combines the data bit string u, the parity bitstring p1 outputted from the first encoder 11, and the parity bit stringp2 outputted from the second encoder 13 by predetermined rules, togenerate an encoded data bit string yk. In the process of combining thedata bit string u, the parity bit string p1, and the parity bit stringp2, the combining unit 14 removes certain bits (as a puncture function)to increase the encoding ratio. The encoded data bit string yk generatedin this manner is outputted from the turbo encoding device. In acommunication system, the encoded data bit string yk is modulated bypredetermined rules, and is transmitted from a transmitter.

The turbo encoding device shown in FIG. 2 has two recursive convolutionencoders (a first encoder 11B and a second encoder 13B) connected inseries. In this structure, the data bit string u is encoded by the firstencoder 11B, and the bit order in the signal string obtained by theencoding is rearranged by the interleaver (π1) 12. The signal stringoutputted from the interleaver (π1) 12 is encoded by the second encoder13, and the signal string obtained by the encoding is outputted as theencoded data bit string yk.

After receiving the signal transmitted from the transmitter in the abovemanner, the receiver decodes the received signal to obtain signal valuestrings U, Y1, and Y2, respectively corresponding to the data bit stringu and the parity bit strings p1 and p2 contained in the encoded data bitstring yk. These signal value strings U, Y1, and Y2 are inputted intothe decoding device corresponding to the turbo encoding device.

In the decoding device, soft output decoding is carried out by twodecoders corresponding to the two encoders 11 and 13 (11B and 13B), andthe soft output information (likelihood information) of each informationbit obtained from one of the two decoders is supplied as a prioriinformation to the other decoder. This operation is repeated by thedecoding device, which has a structure shown in FIG. 3. FIG. 3 shows anexample structure of the decoding device that processes the decodingsignal value strings U, Y1, and Y2 corresponding to the data bit stringu and the parity bit strings p1 and p2 contained in the encoded data bitstring yk outputted from the turbo encoding device shown in FIG. 1.

In FIG. 3, the decoding device includes a first soft input-outputdecoder (SISO: Soft In Soft Out) 21, interleavers (π1) 22 and 23, adeinterleaver (π1⁻¹) 25, a second soft input-output decoder (SISO) 24,and a hard reference unit 26. The first soft input-output decoder 21corresponds to the first encoder 11, and the second soft input-outputdecoder 24 corresponds to the second encoder 13.

The first soft input-output decoder 21 receives the signal value stringsU and Y1 and the a priori information L(u) supplied from the second softinput-output decoder 24. The first soft input-output decoder 21 thencarries out a maximum a posteriori probability (MAP) decoding process toestimate the a posteriori probability of each bit. Here, the aposteriori probability is the probability of a bit uk being 0 or 1 wherethe signal value string is Y(y0, y1, . . . , y1, . . . , yn). In the MAPdecoding process, the log likelihood ratio L(u*) that is the log ratioof the a posteriori probability P (uk|Y) is calculated by the followingformula:L(u*)=L(uk|Y)=ln [P(uk=1|Y)/P(uk=0|Y)]  (1)

In this formula (1), the signal value string Y represents the signalvalue strings U and Y1.

The probability P (uk=1|Y) of the bit uk being 1 and the probability P(uk=0|Y) of the bit uk being 0 are calculated based on the Trelisdiagram that represents the state transition obtained from the signalvalue strings U and Y1.

The log likelihood ratio L(u*) can be represented as follows:L(u*)=Lc·yk+L(uk)+Le(uk)  (2)

wherein

Lc·yk represents the communication path value, with Lc representing theconstant determined by S/N (the communication path value constant) andyk representing the received signal value string of y0, y1, . . . , yn,

L(uk) represents the a priori information that is the known appearanceprobability of the bit uk being 1 or 0, and

Le(uk) represents the external likelihood information obtained withrespect to the bit uk from code restraint.

From the formula (2), the first soft input-output decoder 21 calculatesthe external likelihood information Le(uk) by the following formula:Le(uk)=L(u*)−Lc·yk−L(uk)  (3)

The log likelihood ratio L(u*) calculated in the above described manner(by the formula (1)) is assigned to the formula (3) to obtain theexternal likelihood information Le(uk). The string of the externallikelihood information Le(uk) obtained in this manner is supplied as thestring of the a priori information L(uk) to the second soft input-outputdecoder 24 via the interleaver (π1) 23. The second soft input-outputdecoder 24 also receives the signal value string Y2 as well as thesignal value string U via the interleaver (π1) 22.

Taking the a priori information L(uk) into consideration, the secondsoft input-output decoder 24 calculates a new log likelihood ratio L(u*)by the formula (1). Using the new log likelihood ratio L(u*) and the apriori information L(uk) supplied from the first soft input-outputdecoder 21, the second soft input-output decoder 24 then calculates theexternal likelihood information Le(uk) by the formula (3).

The external likelihood information Le(uk) obtained by the second softinput-output decoder 24 is then supplied as the a priori informationL(uk) to the first soft input-output decoder 21 via the deinterleaver(π1⁻¹) 25. Taking the a priori information L(uk) into consideration, thefirst soft input-output decoder 21 calculates the log likelihood ratioL(u*) and the external likelihood information Le(uk) in the abovedescribed manner. The external likelihood information Le(uk) obtainedhere is used as the a priori information L(uk) for the second softinput-output decoder 24.

In the above described manner, the first soft input-output decoder 21and the second soft input-output decoder 24 repeat the process ofcalculating the log likelihood ratio L(u*), using the externallikelihood information Le(uk) calculated by each other decoder as the apriori information L(uk). This process is referred to as a repetitivedecoding process. In the first process carried out by the first softinput-output decoder 21, the a priori information L(uk) is set at zero(L(uk)=0).

The hard reference unit 26 determines whether the bit uk is 0 or 1,based on the log likelihood ratio L(u*) obtained by the second softinput-output decoder 24 after the decoding process has been repeated apredetermined number of times. If the log likelihood ratio L(u*) ispositive (L(u*)>0), the hard reference unit 26 determines that the bituk is 1 (uk=1). If the log likelihood ratio L(u*) is negative (L(u*)<0),the hard reference unit 26 determines that the bit uk is 0 (uk=0). Thehard reference result is then outputted as a decoding result Uk.

In the above repetitive decoding process, the probability of the bit ukbeing an originally expected value (1 or 0) becomes greater, and theprobability of the bit uk being an unexpected value becomes smaller(i.e., the difference between the probability of the bit uk being 1 andthe probability of the bit uk being 0 becomes greater). The reliabilityof the reference by the hard reference unit 26 increases accordingly.

It is being considered that the turbo encoding and decoding method usedin the communication system as described above should be applied to adata recording and reproducing device such as a magnetic disk device oran optical disk device. Examples of application of the turbo encodingand decoding method to a magnetic disk device are found in “W. E. Ryan,‘Performance of High Rate Turbo Codes on a PR4-Equalized MagneticRecording Channel’, Proc. IEEE Int. Conf. On Communications, pp 947–951,1998”.

In such a data recording and reproducing device, the above describedturbo encoding method is employed in the recording system (the writesystem) for writing data onto a recording medium, and the abovedescribed repetitive decoding method is employed in the reproducingsystem (the read system) for reproducing the data from the recordingmedium. By employing these methods, the high-density data recording onthe recording medium (such as a magnetic disk, an optical disk, anmagneto-optical disk, or magnetic tape) can be reproduced with fewerrors.

The problem with a data reproducing device is generally the noise causedat the time of decoding data. The recording and reproducing propertiesof a data recording and reproducing device such as an optical diskdevice contain low-pass components, and a high-pass filter is normallyused to restrain the noise caused by the low-pass components. Arecording data string has a random bit order, and the cut-off frequencyof the high-pass filter cannot be increased if the signal components ofthe recording string contain low-pass components. For this reason, thenoise caused in the data recording and reproducing device cannot beeffectively restrained.

To solve this problem, there is a known method for restraining thelow-pass components in recording data by modulating the recording dataor convoluting a predetermined bit string (or a parity bit string).According to this method, the low-pass components of a signal to beactually written onto a recording medium can be restrained by the datamodulation or the convolution of a parity bit string, even of therecording data itself contains the low-pass components.

It is possible to apply the technique of data modulation and parity bitstring convolution for removing the low-pass components to a datarecording and reproducing device that rearranges the bit order in datain the data recording process and generates likelihood information (suchas a log likelihood ratio) from a reproduction signal in the datareproducing process, like the above described data recording andreproducing device employing the turbo encoding method and therepetitive decoding method.

In such a data recording and reproducing device, however, the restraintof the low-pass components is not always guaranteed due to therearrangement of the bit order, if the data modulation or the parity bitstring convolution is carried out prior to the bit order rearrangement.On the other hand, if the data modulation or the parity bit stringconvolution is carried out after the data bit order rearrangement,accurate likelihood information corresponding to the actual recordingdata cannot be obtained in the data reproducing process.

Specific references to the prior art relating to the present inventioninclude the following:

-   1) Japanese Laid-Open Patent Application No. 8-287617

This reference teaches a method of uniformly scattering informationwords after a process of rearranging the order of the information wordsin block data. According to this method, adverse influence due to aburst error in a data reproducing process can be reduced.

However, this reference does not teach a method for restraining thelow-pass components in the data to be recorded.

-   2) Japanese Laid-Open Patent Application No. 3-286624

This reference teaches a method of determining such a control codepattern as to restrain the low-pass components in the signal componentsin data when an error detection and correction code is added to a datagroup containing information data and control data.

However, this method does not involve interleaving (or rearrangement) ofthe data.

-   3) Japanese Laid-Open Patent Application No. 6-176495

This reference teaches a method of inserting a bit into every unit wordin data so that desired frequency characteristics can be obtained in theprocess of generating a recording signal.

However, this method does not involve interleaving (or rearrangement) ofthe data either.

-   4) Japanese Laid-Open Patent Application No. 62-030436

This reference teaches a method of restraining the low-pass componentsof the signal components in data by selecting a suitable position ininformation data to which an error detection and correction code isadded.

However, this method does not involve interleaving (or rearrangement) ofthe data either.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide data recordingdevices and data reproducing devices in which the above disadvantagesare eliminated.

A more specific object of the present invention is to provide a datarecording device that can restrain the low-pass components in data to bewritten onto a recording medium, without causing trouble in a datadecoding process using likelihood information.

Another specific object of the present invention is to provide a datareproducing device that can reproduce the data from the recording mediumonto which the data recording has been carried out by the above datarecording device.

The above objects of the present invention are achieved by a datarecording device that carries out encoding procedures including a bitorder rearranging procedure for changing the bit order in data in aprocess of generating a data bit string to be written onto a recordingmedium from original data. This data recording device includes: a databit string combining unit that combines a data bit string obtained priorto a change to the bit order in the bit order rearranging procedure witha plurality of parity bit strings, one by one, by predeterminedcombining rules, so as to generate a plurality of composite data bitstrings; and a data bit string selecting unit that selects one encodeddata bit string, by predetermined criteria, from a plurality of encodeddata bit strings generated by carrying out the encoding proceduresincluding the bit order rearranging procedure for each of the pluralityof composite data bit strings obtained from the data bit stringcombining unit. This data recording device characteristically performs adata write operation onto the recording medium in accordance with theone encoded data bit string selected by the data bit string selectingunit.

In this data recording device, the plurality of composite data bitstrings generated by combining the data bit string with the plurality ofparity bit strings have different change characteristics (or frequencycharacteristics) from one another. The encoding procedures including thebit order rearranging procedure are then carried out for each of theplurality of composite data bit strings to obtain the plurality ofencoded data bit strings of different change characteristics.

One encoded data bit string is then selected from the plurality ofencoded data bit strings of different change characteristics (orfrequency characteristics) by the predetermined criteria, and a datawrite operation is performed on the recording medium based on theselected one encoded data bit string.

The predetermined criteria for selecting one encoded data bit string aredetermined by the low-pass noise characteristics that are allowable in adata reproducing device that restores the original data from therecording medium onto which the data has been written in the abovedescribed manner. To restrict the low-pass noise to the lowest possiblelevel, the criteria should be set in such a manner that the encoded databit string having the low-pass component restricted to the lowestpossible level can be selected.

The encoding procedures are not limited to specific kinds, as long asthe bit order rearranging procedure such as turbo encoding is included.

The above objects of the present invention are also achieved by a datareproducing device that samples a signal reproduced from a recordingmedium in a predetermined cycle to obtain a sampling value string,generates a likelihood information string from the sampling value stringthrough decoding procedures corresponding to the encoding proceduresincluding the bit order rearranging procedure for the above datarecording device, and restores the original data from the likelihoodinformation string. This data reproducing device includes: a hardreference unit that carries out a hard reference process on thelikelihood information string by predetermined criteria, and thenoutputs hard reference data bit strings; and a decoding unit that marksout the bit string corresponding to the parity bit string used in thedata recording device from the hard reference data bit strings outputtedfrom the hard reference unit, and decodes the hard reference data bitstrings using the marked-out bit string by the rules corresponding tothe combining rules employed in the data recording device, therebyrestoring the original data.

The above objects of the present invention are also achieved by a datarecording device that carries out encoding procedures including a bitorder rearranging procedure for changing the bit order in data in aprocess of generating a data bit string to be written onto a recordingmedium from original data. This data recording device includes: aplurality of bit order rearranging units, each of which rearranges, byrearranging rules that are different among the bit order rearrangingunits from one another, the bit order in an encoded data bit stringobtained by encoding the original data by predetermined rules, and thenoutputs a plurality of rearranged encoded data bit strings; an encodeddata bit string selecting unit that selects, by predetermined criteria,one rearranged encoded data bit string from the plurality of rearrangedencoded data bit strings outputted from the plurality of bit orderrearranging units; and a parity adding unit that adds a parity bitstring to a predetermined spot of the one rearranged encoded data bitstring selected by the encoded data bit string selecting unit, so as tomark out the bit order rearranging unit that has outputted the onerearranged encoded data bit string. This data recording devicecharacteristically performs a data write operation onto the recordingmedium in accordance with the one rearranged encoded data bit string, towhich the parity bit string is added by the parity adding unit.

In this data recording device, the bit order in the encoded data bitstring obtained by encoding the original data is rearranged by theplurality of bit order rearranging units to obtain the plurality ofrearranged encoded data bit strings of different bit orders. Theplurality of rearranged encoded data bit strings have different changecharacteristics (or frequency characteristics) from one another. One ofthe rearranged encoded data bit strings of different changecharacteristics is then selected by the predetermined criteria.

A parity bit is attached to the selected rearranged encoded data bitstring, so that the bit order rearranging unit that has outputted theselected rearranged encoded data bit string can be marked out from theother bit order rearranging units. Based on the rearranged encoded databit string provided with the parity bit, a data write operation isperformed on the recording medium

When the data is reproduced from the recording medium on which the datarecording has been carried out in the above manner, the parity bit isextracted to detect the bit order rearranging unit that has been used inthe encoding procedures. Accordingly, a process that corresponds to theprocess carried out by the detected bit order rearranging unit can becarried out in the decoding process carried out in the data reproducingoperation.

The predetermined criteria for selecting one rearranged data bit stringis determined by the low-pass noise characteristics that are allowablein a data reproducing device that restores the original data from therecording medium on which the data write has been carried out. Torestrict the low-pass noise to the lowest possible level, the criteriashould be set in such a manner that the rearranged encoded data bitstring having the low-pass component restricted to the lowest possiblelevel can be selected.

In this data recording device, the encoding procedures are not limitedto specific kinds, as long as the bit order rearranging procedure suchas turbo encoding is included.

The above objects of the present invention are also achieved by a datareproducing device that samples a signal reproduced from a recordingmedium in a predetermined cycle to obtain a sampling value string,generates a likelihood information string from the sampling value stringthrough decoding procedures corresponding to the encoding proceduresincluding the bit order rearranging procedure for the above datarecording device, and then restores the original data from thelikelihood information string. This data reproducing device includes: aplurality of information order rearranging units that change the orderin the likelihood information string obtained through the decodingprocedures by different rearranging rules, and output differentrearranged likelihood information strings; and a selecting unit thatgenerates a bit string corresponding to a parity bit string used in thedata recording device from the likelihood information string obtainedthrough the decoding procedures, and selects one information orderrearranging unit that is represented by the bit string from theplurality of information order rearranging units. The one informationorder rearranging unit selected by the selecting unit performs an orderrearranging operation on the likelihood information string in a processof restoring the original data from the sampling value string.

The above and other objects and features of the present invention willbecome more apparent from the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example structure of a conventionalturbo encoding device;

FIG. 2 is a block diagram showing another example structure of aconventional turbo encoding device;

FIG. 3 is a block diagram showing an example structure of a decodingdevice corresponding to the turbo encoding device of FIG. 1;

FIG. 4 shows a data recording and reproducing device as an embodiment ofthe present invention;

FIG. 5 is a block diagram showing an example structure of the recordingdata string generator of the data recording and reproducing device ofFIG. 4;

FIG. 6 shows an example operation of the parity convolution circuit ofthe data recording and reproducing device of FIG. 4;

FIG. 7 is a block diagram showing an example structure of each of theencoding circuits of the recording data string generator of FIG. 5;

FIG. 8 shows an example structure of the encoder of each of the encodingcircuits of FIG. 7;

FIG. 9 is a block diagram showing an example structure of the repetitivedecoder of the data recording and reproducing device of FIG. 4;

FIG. 10 shows an example operation of the convolution decoding circuitof the repetitive decoder of FIG. 9;

FIG. 11 is a block diagram showing another example structure of therecording data generator of the data recording and reproducing device ofFIG. 4;

FIG. 12 is a block diagram showing another example structure of therepetitive decoder of the data recording and reproducing device of FIG.4; and

FIG. 13 is a block diagram showing an example structure for embodying are-selecting function of the interleaver in the repetitive decoder ofFIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of embodiments of the present invention,with reference to the accompanying drawings.

FIG. 4 shows a data recording device and a data reproducing device as anembodiment of the present invention. In FIG. 4, the data recordingdevice is embodied by the write system of a data recording andreproducing device that records data onto a recording medium (amagneto-optical disk), while the data reproducing device is embodied bythe read system of the data recording and reproducing device.

The data recording and reproducing device shown in FIG. 4 is an opticaldisk device that employs a magneto-optical (MO) disk 110 as a recordingmedium, and includes a recoding and reproducing mechanism 100, the writesystem for writing data onto the magneto-optical disk 110, and the readsystem for reproducing the data from the magneto-optical disk 110. Therecording and reproducing mechanism 100 includes an optical beam outputunit such as a laser diode, an optical head (not shown) equipped with aphotodetector such as a photo diode, and a disk driver 120 that rotatesthe magneto-optical disk 110 at a predetermined speed.

The write system includes a recording data string generator 30 and LDdriver circuit 31. The recording data string generator 30 carries outoperations such as a parity-bit convolution process and an encodingprocess onto user data uk, and generates an encoded data bit string ci′that is to be written onto the magneto-optical disk 110. The LD drivercircuit 31 performs a driving control operation on the optical beamoutput unit of the recording and reproducing mechanism 100, based on theencoded data bit string ci′. Signal write is carried out onto themagneto-optical disk 110 by the optical beam emitted from the opticalbeam output unit that is controlled based on the encoded data bit stringci′. This signal writing onto the magneto-optical disk 110 is carriedout at such a high density as to cause predetermined waveforminterference when the signal is reproduced.

FIG. 5 shows the structure of the recording data string generator 30.

In FIG. 5, the recording data string generator 30 includes a parityconvolution circuit 310, a plurality of encoding circuits 320-1 through320-2 ^(n), and a select circuit 330. The parity convolution circuit 310convolutes a predetermined parity bit string into the user data uk, sothat the low-pass component of the data bit to be written onto themagneto-optical disk 110 can be restricted. In this convoluting process,a parity bit string of n bits is convoluted into user data of N bits.More specifically, the user data uk is divided into divisional bitstrings A, B, C, . . . , each of which consists of n bits. The paritybit string of n bits and the first divisional bit string A areconvoluted (an exclusive OR operation for each bit) to generate aconvoluted bit string A′. The convoluted bit string A′ and the seconddivisional bit string B are then convoluted to generate the nextconvoluted bit string B′. Thereafter, every time a new convoluted bitstring is generated, the new convoluted bit string and the nextdivisional bit string are convoluted in the same manner. As a result, aconvolutional data bit string uk′ having the parity bit string of n bitsfollowed by the convolutional data bit strings A′, B′, C′, . . . isobtained.

There are 2^(n) kinds of parity bit strings each consisting of n bits.The parity convolution circuit 310 carries out the above describedconvoluting process for all the parity bit strings. The parityconvolution circuit 310 outputs 2^(n) of convolutional data bit stringsuk′, each of which is then supplied to each corresponding one of theencoding circuits 320-1 through 320-2 ^(n). Each of the encodingcircuits 320-1 through 320-2 ^(n) carries out operations such as anencoding process and an interleaving process on the convolutional databit string uk′. FIG. 7 shows an example structure of each of theencoding circuits 320-1 through 320-2 ^(n).

In FIG. 7, each of the encoding circuits 320-1 through 320-2 ^(n)includes an encoder 321, a coupler 322, and an interleaver (π) 323. Theencoder 321 is a recursive structure convolution encoder that includestwo delay elements 3211 and 3212 and two exclusive OR gates 3215 and3216 as shown in FIG. 8. The encoder 321 performs an encoding operationwith a restraint length of 3 on the convolutional data bit string uk′supplied from the parity convolution circuit 310, so as to generate aparity bit string pk corresponding to the convolutional data bit stringuk′.

The coupler 322 couples the convolutional data bit string uk′ with theparity bit string pk generated from the encoder 321 by predeterminedrules, and then removes certain bits from the bit string obtained fromthe coupling process by predetermined rules (also known as a puncturingfunction), so as to generate an encoded data bit string ai′. Theinterleaver (π) 323 rearranges the encoded data bit string ai′ providedfrom the coupler 322 by predetermined rules, so as to generate theencoded data bit string ci′.

Referring back to FIG. 5, the recording data string generator 30 selectsone encoded data bit string ci′ from the encoded data bit stringsoutputted from the encoding circuits 320-1 through 320-2 ^(n). Morespecifically, the recording data string generator 30 calculates the DSV(Digital Sum Variation) of each of the encoded data bit stringsoutputted from the encoding circuits 320-1 through 320-2 ^(n), and thenselects the encoded data bit string ci′ that has the DSV of the smallestmaximum absolute value.

The DSVs are parameters representing variations of signals. With asignal having a short variation cycle (i.e., having a large amount ofhigh-pass components), the maximum absolute value of the DSV is small.With a signal having a long variation cycle (i.e., having a large amountof low-pass components), the maximum absolute value of the DSV is large.Accordingly, the select circuit 330 selects the encoded data bit stringhaving the smallest amount of low-pass components among the encoded databit strings generated from the encoding circuits 320-1 through 320-2^(n).

As described above, in the write system of the data recording andreproducing device, the user data uk is processed by N bits. In thatprocess, the encoded data bit string ci′ having the low-pass componentthat is restrained by the convoluting process of n-bit parity bitstrings is supplied to the LD driver circuit 31. The encoded data bitstring ci′ is then written onto the magneto-optical disk 110 by theabove described operation of the LD driver circuit 31.

The above convoluting process, the calculation of the DSVs, and theselection of the encoded data bit string can be carried out not insynchronization with the write operation of the LD driver circuit 31. Tominimize the delay due to those processes and operations, they can becarried out in synchronization with a clock of a higher speed than thesynchronous clock for the data write.

Referring back to FIG. 4, the read system of the data recording andreproducing device includes an amplifier 41, an AGC (Auto GainController) 42, a low-pass filter 43, an equalizer 44, and ananalog-digital (A-D) converter 45. An MO reproduction signal outputtedfrom the photodetector of the recording and reproducing mechanism 100 isshaped into a waveform that can be regarded as a PR (Partial Response)waveform by the amplifier 41, the AGC 42, the low-pass filter 43, andthe equalizer 44. In other words, a reproduction signal from themagneto-optical disk 110 is substantially encoded in a PR channel.Accordingly, the write system (the encoder 321 of each of the encodingcircuits 320-1 through 320-2 ^(n)) and the substantial encoding functionof the PR channel embody the structure of the turbo encoding deviceshown in FIG. 2.

The read system further includes a memory unit 46, a repetitive decoder47, and a controller 48. The signal that has been subjected to the abovewaveform equalizing process is converted into a digital value (asampling value) by the A-D converter 45 in a predetermined cycle, andthe sampling value yi outputted from the A-D converter 45 is stored inthe memory unit 46. The sampling value yi stored in the memory unit 46is then decoded by the repetitive decoder 47 (a turbo decoding process).The controller 48 controls the operation and the decoding conditions ofthe repetitive decoder 47. The repetitive decoder 47 restores the userdata string uk in a repetitive decoding process, and then outputsthe-user data string uk.

The repetitive decoder 47 has a decoder corresponding to the encoder 321(see FIGS. 5 and 7) of each encoding circuit in the write system and theencoding function of the PR channel. FIG. 9 shows an example structureof the repetitive decoder 47.

In FIG. 9, the repetitive decoder 47 includes a PR channel decoder 471,a deinterleaver (π⁻¹) 472, a disassembler 473, a code decoder 474, acoupler 475, an interleaver (π) 476, a hard reference unit 477,subtractors 478 and 479, and a convolution decoding circuit 4710.

The PR channel decoder 471 is a decoder corresponding to the abovedescribed encoding function of the PR channel, and carries out an aposteriori probability decoding process (APP). More specifically, with asampling value Y (y1, y2, . . . , yn) being detected, a log likelihoodratio L (ci*) based on the ratio of the probability P of the bit cibeing 1 (ci=1|Y) to the probability P of the bit ci being 0 (ci=0|Y) iscalculated.L(ci*)=ln [P(ci=1|Y)/P(ci=0Y)]  (4)

Each of the above probabilities can be calculated based on the Trelisdiagram that represents the state transition of the sampling value yi.

Being calculated from the above equation (4), the log likelihood ratioL(ci*) is represented by a numeric value in a continuous range of apositive numeric value Lmax to a negative numeric value Lminrepresenting the probability range of the maximum probability of the bitci being 1 to the maximum probability of the bit ci being 0.

Likelihood information L(ci*) outputted from the PR channel decoder 471is subtracted from a priori information La(ci) based on the output fromthe code decoder 474 (described later) by the subtractor 478 to obtainexternal likelihood information Le(c).

The order in the string of external likelihood information Le(c) isrearranged by the deinterleaver (π⁻¹) 472, and is then sent to thedisassembler 473. The disassembler unit 473 disassembles the string oflikelihood information into a string of likelihood information L(uk)with respect to the user data bits uk and a string of likelihoodinformation L(pk) with respect to the parity bits pk. At the time ofdisassembling, information is added (a depuncturing function) by therules corresponding to the puncturing (the puncturing function of thecoupler 322) rules in the encoding process.

The code decoder 474 is a decoder corresponding to the encoder 321 ofeach of the encoding circuits 320-1 through 320-2 ^(n) in the writesystem, and carries out the a posteriori probability decoding process(APP). More specifically, the code decoder 474 calculates the loglikelihood ratio L(u*) represented by the a posteriori probabilities(the probability of uk being 1 and the probability of uk being 0) withrespect to the user data bits uk, and the log likelihood ratio L(p*)represented by the a posteriori probabilities (the probability of pkbeing 1 and the probability of pk being 0) with respect to the paritybits, based on the a priori information L(uk), which is the likelihoodinformation of the user data bits, and the a priori information L(pk),which is the likelihood information of the parity bits, respectively.

The string of the log likelihood ratios L(u*) and the string of the loglikelihood ratios L(p*) successively outputted from the code decoder 474are supplied to the coupler 475. The coupler 475 couples the string ofthe log likelihood ratios L(u*) with the string of the log likelihoodratios L(p*), and removes certain information from the coupledinformation by the predetermined rules (the puncturing function). As aresult, likelihood information L(c*) is outputted from the coupler 475.

The a priori information Le(c) (prior to the disassembling into theinformation L(uk) and L(pk)) to be supplied to the code decoder 474 issubtracted from the above likelihood information L(c*) by the subtractor479. The result is supplied to the interleaver (π) 476.

The string of the likelihood information rearranged by the interleaver(π) 476 is supplied as the a priori information La(ci) to the PR channeldecoder 471, and is also sent to the subtractor 478.

In the manner described above, the repetitive decoder 47, which has thePR channel decoder 471 and the code decoder 474, carries out therepetitive decoding process, with one of the two decoders using the apriori information supplied from the other decoder.

The hard reference unit 477 determines whether each user data bit Uk′ is1 or 0, based on the log likelihood ratio L(u*) with respect to the databit uk outputted from the code decoder 474 after the repetitive decodingprocess has been repeated a predetermined number of times. The hardreference unit 477 then outputs each data bit Uk′ of the determinedvalue. As described above, the log likelihood ratio L(u*) is representedby a positive number when the probability of the bit uk being 1 isgreater than the probability of the bit uk being 0, and by a negativenumber when the probability of the bit uk being 1 is smaller than theprobability of the bit uk being 0. Accordingly, the hard reference unit477 actually uses a slice level of “0” to carry out the hard referenceprocedure based on the log likelihood ratio L(u*), and generates thedata bits Uk′.

The data bits Uk′ outputted from the hard reference unit 477 correspondto the convolutional data bit string uk′ (shown in FIG.6) generated inthe recording data generator 30. The data bit string Uk′ correspondingto the convolutional data bit string uk′ is then supplied to theconvolution decoding circuit 4710. The convolution decoding circuit 4710carries out a decoding process for the data bit string Uk′ supplied fromthe hard reference unit 477, by the process rules corresponding to theprocess rules for the convolution carried out by the parity convolutioncircuit 310 (shown in FIG. 5).

In this decoding process, the hard reference data (i.e., the data bitstring Uk′) outputted from the hard reference unit 477 is divided intobit strings by n bits, as shown in FIG. 10. As a result, an n-bit paritybit string is located at the top, followed by n-bit convolutional bitstrings A′, B′, C′, . . . . The parity bit string at the top isconvoluted with the next convolutional bit string A′ (an exclusive ORoperation) to restore the original divisional bit string A. Theconvolutional bit string A′ is then convoluted with the nextconvolutional bit string B′ to restore the original divisional bitstring B. In the same manner, each two neighboring convolutional bitstrings are convoluted with each other. As a result, restored data Ukcorresponding to the N-bit user data having the divisional bit stringsA, B, C, . . . is obtained.

In the write system of the above described data recording andreproducing device, the user data uk to be recorded and the parity bitstrings of 2^(n) kinds are convoluted with each other to generate theconvolutional bit strings uk′ of 2^(n), with the parity bit string beingadded to the top. The encoded data bit strings ci′ of 2^(n) are thengenerated from the convolutional bit strings uk′ of 2^(n). From theencoded data bit strings ci′ of 2^(n), the encoded data bit string thathas the smallest maximum absolute value of the DSV is selected. In otherwords, the encoded data bit string having the most restrained low-passcomponent among the encoded data bit strings ci′ of 2^(n) is selected asthe data bit string to be written.

In the read system of the data recording and reproducing device, thedata bit string Uk′ is restored from the magneto-optical disk 110, onwhich the selected encoded data bit strings have been written, by therepetitive decoding method. The data bit string Uk′ is then decoded bythe convoluting rules using the parity bit string located at the top ofthe data bit string Uk′. As a result, the restored data Uk is obtainedfinally.

In this data recordings and reproducing device, the encoding bit stringhaving restrained low-pass components are written on the magneto-opticaldisk 110, even though the bit order is rearranged by the interleaverafter the parity bit convolution process is carried out for the userdata uk. Accordingly, the low-pass noise in a reproduction signal fromthe magneto-optical disk 110 should be restrained. Furthermore, sincethe convolutional data bit strings including the parity bit string aresmoothly restored by the repetitive decoding process using thelikelihood information (i.e., the log likelihood ratios), the originaluser data can be restored by carrying out the convolution encodingprocess for the convolutional data bit strings using the parity bitstring.

The recording data string generator 30 may have a structure shown inFIG. 11. In this modification, a single encoder and a plurality ofinterleavers of different characteristics are employed.

In FIG. 11, the recording data string generator 30B includes a singleencoder 321B, a coupler 322B, and a plurality (2^(n), for example) ofinterleavers 323-1 through 323-2 ^(n)), a selecting circuit 340, and aparity adding circuit 350. Like the encoder 321 of the recording datastring generator 30, the encoder 321B is a recursive structureconvolution encoder, and generates a parity bit string pk correspondingto the user data uk. Like the coupler 322, the coupler 322B couples theuser data uk with the parity bit string pk supplied from the encoder321B by the predetermined rules. The coupler 322B then removes certainbits from the coupled bit string (the puncture function) by thepredetermined rules, and generates an encoded data bit string ai.

Each of the interleavers 323-1 through 323-2 ^(n) rearranges the bitorder of the encoded data bit string ai supplied from the coupler 322 bythe order rearranging rules that differ among the interleavers 323-1through 323-2 ^(n). The selecting circuit 340 calculates the DSVs of theencoded data bit strings outputted from the interleavers 323-1 through323-2 ^(n), and selects the encoded data bit string having the smallestmaximum absolute value of the DSVs. The selecting circuit 340 suppliesthe parity adding circuit 350 with the selected encoded data bit stringand the information for marking out the interleaver that has outputtedthe selected encoded data bit string.

The parity adding circuit 350 adds an n-bit parity bit string (which canrepresent 2^(n) kinds of information) representing the information formarking out the above interleaver from the others, to a predeterminedposition (at the top, for example) of the encoded data bit stringsupplied from the selecting circuit 340. The parity adding circuit 350thus generates the encoded data bit string ci′ to be written onto themagneto-optical disk 110.

The repetitive decoder of the read system corresponding to the writesystem of the recording data string generator 30B having the abovedescribed structure may have a structure shown in FIG. 12.

In FIG. 12, the repetitive decoder 47B has the same turbo-decodingstructure as shown in FIG. 9, except that a selective control circuit4711 is employed instead of the convolution decoding circuit 4710 in thestructure shown in FIG. 9, a deinterleaver set 4720 consisting of aplurality of deinterleavers corresponding to the plurality ofinterleavers 323-1 through 323-2 ^(n) of the recording data stringgenerator 30B is employed instead of the single deinterleaver 472, andan interleaver set 4760 consisting of a plurality of interleaverscorresponding ot the plurality of interleavers 323-1 through 323-2 ^(n)is employed instead of the single interleaver 476.

In this repetitive decoder 47B, the selective control circuit 4711carries out a hard reference procedure on the log likelihood ratioL(ci*) outputted as the a posteriori probability information from a PRchannel decoder 471B, and then generates a decoded bit string. Theselective control circuit 4711 further extracts, from the decoded bitstring, the parity bit string that has been added to the predeterminedposition and represents the information for marking out the interleaver.The selective control circuit 4711 then selects, from the deinterleaverset 4720 and the interleaver set 4760, the deinterleaver and theinterleaver corresponding to the interleaver distinguished by theextracted parity bit string.

The selected deinterleaver and the interleaver become valid in therepetitive decoder 47B. Using the deinterleaver and the interleavercorresponding to the interleaver used in the encoding process of therecording data string generator 30 of the write system, the repetitivedecoder 47 carries out the repetitive decoding process, following thesame procedures as described earlier in this specification.

When extracting the parity bit string that distinguishes theinterleaver, the selective control circuit 4711 removes the string ofthe log likelihood ratios (the likelihood information) corresponding tothe parity bit string from the string of the log likelihood ratiossuccessively outputted from the PR channel decoder 471B. Thereafter, theabove described repetitive decoding is carried out based on the stringof the log likelihood ratios without the log likelihood ratioscorresponding to the parity bit string.

In the write system of this data recording and reproducing device, thebit order in the encoded data bits ai obtained by encoding the user datauk to be recorded is rearranged by each of a plurality (2^(n), forexample) of interleavers. From a plurality of encoded data bit stringsobtained as a result of the rearrangement of the bit order, the encodeddata bit string having the smallest maximum absolute value of the DSVsis selected. A parity bit string representing the information formarking out the interleaver used for the selected encoded data bitstring is then added to a predetermined spot of the selected encodeddata bit string, so that the encoded data bit string ci′ to be writtenonto the magneto-optical disk 110 is generated. In this manner, theparity bit string and the encoded data bit string having the mostrestrained low-pass component among the plurality of encoded data bitstrings are integrally written onto the magneto-optical disk 110.

In the read system of this data recording and reproducing device, theparity bit string is extracted from a decoded bit string obtained from ahard reference process carried out on the likelihood information stringsupplied from the PR channel decoder 471B, and the interleaver and thedeinterleaver distinguished by the parity bit string are selected from aplurality of interleavers and a plurality of deinterleavers. Therepetitive decoding process is then carried out, using the selectedinterleaver and deinterleaver.

With this data recording and reproducing device, encoded data bitstrings having more restrained low-pass components are written onto themagneto-optical disk 110, and the user data can be smoothly restoredfrom the magneto-optical disk 110 by the repetitive decoding method.

However, if an error occurs in the hard reference process carried out bythe selective control circuit 4711 for the likelihood informationsupplied from the PR channel decoder 471B, the deinterleaver and theinterleaver corresponding to the interleaver selected in the writesystem cannot be selected. An error correcting process to be carried outin such a case will be described below.

A check bit is added beforehand to each encoded data bit string ci′ tobe written onto the magneto-optical disk 110. As shown in FIG. 13, thecontroller 48 has a CRC (Cycle Redundancy Check) unit 48 a. The CRC unit48 a carries out a CRC based on the check bit contained in the decodeddata outputted from the repetitive decoder 47B shown in FIG. 12, so asto determine the bit error rate of the decoded data. Based on the biterror rate determined by the CRC unit 48 a, the controller 48 suppliesthe repetitive decoder 47B with a control signal for re-selecting aninterleaver and a deinterleaver. Upon receipt of the control signal forre-selecting, the repetitive decoder 47B selects a suitabledeinterleaver and a suitable interleaver from the deinterleaver set 4720and the interleaver set 4760, and then carries out the repetitivedecoding process again.

If the repetitive decoder 47B selects a wrong deinterleaver and a wronginterleaver, the decoding result is as full of errors as in a case wherea hard reference process is carried out for the likelihood informationequivalent to a probability of ½. Therefore, the controller 47 caneasily re-select a deinterleaver and an interleaver, based on the biterror rate determined by the CRC unit 48 a. If the bit error conditionhas not reached a predetermined level, the above described procedure forre-selecting a deinterleaver and an interleaver is repeated.

In this manner, even if an error repeatedly occurs in the hard referenceprocess carried out by the selective control circuit 4711 for thelikelihood information supplied from the PR channel decoder 471, thedeinterleaver and the interleaver corresponding to the interleaverselected in the write system can be selected, and the user data can beaccurately restored.

Although the data recording and reproducing device employs the turboencoding and decoding method in the above described embodiments, thepresent invention is not limited to any particular encoding and decodingmethod, as long as the bit order in a data bit string is rearranged inthe encoding process.

Also, the structure of the above described write system can be appliedto a device for data recording only, while the structure of the abovedescribed read system can be applied to a device for data reproducingonly.

In each of the above described embodiments, the parity convolutingcircuit 310 shown in FIG. 5 can be referred to as a data bit stringcombining unit, and the selecting circuit 330 shown in FIG. 5 can bereferred to as a data bit string selecting unit. The convolutiondecoding circuit 4710 shown in FIG. 9 can also be referred to as adecoding unit.

The interleavers 323-1 through 323-2 n shown in FIG. 11 can also bereferred to as a plurality of bit order rearranging units, and theselecting circuit 340 shown in FIG. 11 can also be referred to as anencoded data bit string selecting unit. The deinterleaver set 4720 andthe interleaver set 4760 shown in FIG. 12 can also be referred to as aplurality of information order rearranging units, and the selectivecontrol circuit 4711 shown in FIG. 12 can also be referred to as aselecting unit.

It should be noted that the present invention is not limited to theembodiments specifically disclosed above, but other variations andmodifications may be made without departing from the scope of thepresent invention.

1. A data recording device that carries out encoding proceduresincluding a bit order rearranging procedure for changing the bit orderin data in a process of generating a data bit string to be written ontoa recording medium from original data, said data recording devicecomprising: a data bit string combining unit that combines a data bitstring obtained prior to a change to the bit order in the bit orderrearranging procedure with a plurality of parity bit strings, one byone, by predetermined combining rules, so as to generate a plurality ofcomposite data bit strings; and a data bit string selecting unit thatselects one encoded data bit string, by predetermined criteria, from aplurality of encoded data bit strings generated by carrying out theencoding procedures including the bit order rearranging procedure foreach of the plurality of composite data bit strings obtained from thedata bit string combining unit, said data recording device performing adata write operation onto the recording medium in accordance with theone encoded data bit string selected by the data bit string selectingunit.
 2. The data recording device as claimed in claim 1, wherein thedata bit string combining unit combines the original data with theplurality of parity bit strings one by one.
 3. The data recording deviceas claimed in claim 1, wherein the data bit string combining unitconvolutes the data bit string obtained prior to the change to the bitorder in the bit order rearranging procedure with the plurality ofparity bit strings, one by one, by predetermined rules, so as togenerate a plurality of convolutional data bit strings as the pluralityof composite data bit strings.
 4. The data recording device as claimedin claim 1, wherein the data bit string selecting unit calculates apredetermined parameter representing change characteristics of each ofthe plurality of encoded data bit strings, and then selects one encodeddata bit string in accordance with the predetermined parametercalculated from each of the plurality of encoded data bit strings.